This invention relates to overhead-valve (OHV) engines, and more particularly it is concerned with an OHV engine equipped with an improved breather device.
An OHV type cylinder is known which has a suction valve and a discharge valve located on the top surface of the combustion chamber, and an OHV V-type engine is used which comprises a plurality of OHV cylinders arranged in the form of a letter V.
In this type of engine, a camshaft is usually located above the crankshaft near each cylinder, and tappets and push rods for actuating the suction valve and discharge valve are located along an upper portion of each cylinder.
A four-cycle engine including the aforesaid type of engine is provided with means for releasing blowby gas leaking from the surfaces of the cylinders in which pistons are fitted to a crank chamber (an interior space of the crankcase) or a breather device operative to effect ventilation for the crank chamber.
If unattended, the blowby gas would cause an inordinate rise in the pressure in the crank chamber, causing the engine oil to leak. Thus, it is customary to provide a breather device for releasing the blowby gas through a check valve. The blowby gas usually contains non-combusted fuel components which would cause air pollution if released to the atmosphere, so that the blowby gas is usually led to the air cleaner.
Agitation of the oil in the crank chamber usually results in oil mist mingling with the blowby gas. Thus, to avoid air pollution, ejection of white fumes and accumulation of carbon, it has been usual practice to return the blowby gas to the air cleaner after subjecting same to oil/gas separation. In order that the breather device may satisfactorily perform the function of releasing the blowby gas, it is necessary that it be located in an upper portion of the crankcase.
Japanese Utility Model Examined Publication No. 234567/81 discloses one example of the construction of the breather device of an OHV V-type engine of the prior art.
Generally, the breather devices of the OHV V-type engines have each been constructed as an entity separate from the crankcase and mounted in an upper portion of the gear chamber of the crankcase or at one side of the gear chamber which projects from the top of the crankcase. This constructional form has given rise to several problems. One of them is that it is impossible to provide an oil/gas separation chamber of sufficiently large volume to satisfactorily achieve separation of oil from gas. Another problem is that, since various parts are mounted at the bottom of the V-bank (the junction of the upper sides of the cylinders arranged in the form of a letter V), dust and pieces of straw tend to collect therein and difficulty is experienced in performing a cleaning operation.
Proposals have been made to lead the blowby gas to the rocker arm chamber to lubricate the interior thereof and push rods and other parts for actuating the suction and discharge valves by utilizing the oil mist in the blowby gas. However, since the breather device of the prior art makes it necessary to provide an additional passageway or pipe for the gas flowing from the rocker arm chamber to the oil/gas separation chamber, the problem that the engine becomes complex in construction has arisen.